1. Field of the Invention
This invention relates to a resistor layer for a field emission device and the like, and more particularly, to a resistor layer that prevents shorting in a field emission display baseplate.
2. Description of the Related Art
A field emission device (FED) typically includes an electron emission tip configured for emitting a flux of electrons upon application of an electric field to the field emission device. An array of miniaturized field emission devices can be arranged on a plate and used for forming a visual display on a display panel. Indeed, field emission devices have been shown to be a promising alternative to cathode ray tube display devices. For example, field emission devices may be used in making flat panel display devices for providing visual display for computers, telecommunication and other graphics applications. Flat panel display devices typically have a greatly reduced thickness compared to the generally bulky cathode ray tubes.
Field emission display devices are currently being touted as the flat panel display type poised to take over the liquid crystal display (LCD) market. FEDs have the advantages of being lower in cost, with lower power consumption, having a better viewing angle, having higher brightness, having less smearing of fast moving video images, and being tolerant to greater temperature ranges than other display types.
One problem with FEDs has been the shorting of the resistor layer. In the FED structure, a resistor layer is typically provided over a metallic layer in an FED baseplate. Conventional materials used are a boron-doped amorphous silicon for the resistor layer, and chromium, aluminum, aluminum alloys or a combination of such materials for the metallic layer. Short-circuiting of the device may occur in this structure because of diffusion of silicon from the resistor layer into the metal at temperatures above about 300xc2x0 C. This problem is especially prevalent when the resistor layer is deposited directly over an aluminum layer. Diffusion of silicon into the aluminum will take place, for instance, during deposition at temperatures from about 330 to 400xc2x0 C., or during packaging of the baseplate at temperatures of about 450xc2x0 C. This diffusion problem is caused primarily because Si forms a eutectic contact with Al above 400xc2x0 C., and also because the free energy of silicon is higher in its amorphous state.
Another problem is that resistor layers made of boron-doped amorphous silicon cause nucleation related defects at the interface of the resistor and metal, especially when the metal is chromium. In an FED structure using a chromium metallic layer, for instance, the interaction of diborane gas at the chromium surface causes irregularities at the surface between the metal and resistor. Discontinuities in the resistor layer can cause the loss of the benefits for which the resistor layer was used in the first place. Additionally, discontinuities in the resistor layer can present problems when subsequent etching or photolithographic processes are conducted, potentially causing delamination of various layers and other irregularities.
Accordingly, what is needed is an improved resistor having fewer defects and discontinuities to prevent short-circuiting in FED devices and the like.
Briefly stated, the needs addressed above are solved by providing an amorphous silicon resistor layer doped with nitrogen and phosphorus over a metallic layer of aluminum, chromium, or both. For instance, in an FED structure having either a metallic layer of aluminum or a chromium/aluminum bilayer, a nitrogen-phosphorous-doped silicon resistor layer is deposited over the metal. The use of nitrogen-doped silicon solves the problems stated above because the Nxe2x80x94Si bond is longer and stronger than the Bxe2x80x94Si bond. Therefore, Si is less likely to diffuse out of the resistor layer into the aluminum to cause short-circuiting. Furthermore, the strength of the Nxe2x80x94Si bond makes the atoms in the resistor layer less mobile, thereby diminishing the nucleation problem at the resistor/metal interface.
In one aspect of the present invention, a resistive structure is provided comprising a metallic conductive layer and a resistor layer over the conductive layer. The resistor layer comprises nitrogen-doped amorphous silicon, preferably with about 5 to 15 atomic percent nitrogen. The metallic conductive layer is preferably selected from the group consisting of an aluminum layer, a chromium layer and an aluminum/chromium bilayer.
In another aspect of the present invention, a field emission display device is provided comprising a substrate and a conductive layer over the substrate. An amorphous silicon resistor layer is provided over the conductive layer, the resistor layer being doped with nitrogen and phosphorus. A dielectric layer is provided over the resistor layer. A gate electrode is provided over the dielectric layer, the gate electrode including a gate conductive layer.
In another aspect of the present invention, a resistor layer is provided for field emission devices, comprising amorphous silicon doped with at least about five atomic percent nitrogen. The resistor layer also preferably has a phosphorus concentration of about 1xc3x971020 and 5xc3x971020 atoms/cm3.
In another aspect of the present invention, a method is provided for forming a resistive structure. A conductive layer is formed over a substrate. A resistor layer is formed over the conductive layer, the resistor layer being formed of amorphous silicon having dopants of nitrogen and phosphorus. In one preferred embodiment, the resistor layer is formed by introducing gases of NH3, PH3, SiH4 and H2. The NH3 gas is preferably introduced at a rate of about 35 and 120 sccm. The PH3 gas is preferably introduced at a rate of about 50 to 100 sccm. The SiH4 gas is preferably introduced at a rate of about 500 sccm.